JP4433508B2 - Control device for spark ignition direct injection engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes a spark ignition type equipped with an injector that directly injects fuel into a combustion chamber, and a NOx catalyst that stores NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases in an engine exhaust passage. The present invention relates to a control device for a direct injection engine.
[0002]
[Prior art]
Conventionally, in a spark ignition type direct injection engine that has been provided with an injector that directly injects fuel into a combustion chamber and that performs lean operation by stratified combustion in order to improve fuel efficiency in a low load region, it stores NOx in an oxygen-excess atmosphere and oxygen A NOx catalyst that releases NOx as the concentration decreases is provided in the exhaust passage, and this NOx catalyst purifies NOx even during lean operation. When such a NOx catalyst is provided, it is necessary to release the NOx from the NOx catalyst at an appropriate time to refresh the NOx catalyst and to reduce the released NOx. For this catalyst refresh and reduction of the released NOx, Therefore, it is required to enrich the air-fuel ratio of the exhaust and increase the amount of CO and HC in the exhaust as a reducing material.
[0003]
An engine that performs lean operation by stratified combustion in the stratified combustion region on the low load side, while injecting fuel in the intake stroke while keeping the air-fuel ratio below the stoichiometric air-fuel ratio in the homogeneous combustion region of higher load than this Then, at least at the time of acceleration from the stratified combustion region to the uniform region, the NOx catalyst is refreshed by enriching the air-fuel ratio. Further, when the lean operation in the stratified combustion mode is continued and the NOx occlusion amount of the NOx catalyst is increased to a predetermined value or more, even in the stratified combustion region, the air-fuel ratio is enriched below the stoichiometric air-fuel ratio for a predetermined time. There is also known a catalyst designed to refresh the catalyst.
[0004]
[Problems to be solved by the invention]
By the way, when switching from the stratified combustion combustion mode to the uniform combustion mode, for example, when accelerating the transition from the stratified combustion region to the uniform combustion region, the throttle opening is reduced at the time of mode switching to reduce the intake charge amount for torque adjustment. The air-fuel ratio is made rich by this, but at this time, there is a considerable delay from when the throttle opening is controlled until the intake charge amount actually decreases, and during this delay period Is in a state where the intake charge amount is larger than the appropriate value in the uniform combustion mode. In this state, if the fuel injection is switched to the intake stroke injection and the fuel injection amount is increased to enrich the air-fuel ratio, a sudden change in torque occurs.
[0005]
For this reason, as fuel injection control, the compression stroke injection state is maintained at the lean air-fuel ratio during the delay period, and the intake charge amount is sufficiently decreased after the delay period has elapsed, and then the stoichiometric air-fuel ratio or less. By switching to the state in which the intake stroke injection is performed, the sudden change in torque is prevented. However, from the viewpoint of refreshing the NOx catalyst, NOx is released from the NOx catalyst and the released NOx is reduced only by controlling the air-fuel ratio to be rich after the intake charge amount decreases. The effect of reducing is not always obtained sufficiently.
[0006]
Thus, if the air-fuel ratio of the exhaust gas is enriched with a large amount of exhaust gas guided to the NOx catalyst using the delay period, a large amount of CO and HC can be supplied to the NOx catalyst, The promotion of NOx reduction can be expected.
[0007]
As a technique for promoting the refresh of the catalyst, for example, as disclosed in Japanese Patent Laid-Open No. 10-274085, when the NOx occlusion amount of the NOx catalyst is not less than a predetermined value and the air-fuel ratio is in a lean operation state, stratification is performed. In addition to the main injection for combustion, there is one in which additional fuel is injected during the expansion stroke to generate CO. Further, as disclosed in JP-A-4-231645, HC is supplied to the catalyst by performing a small amount of sub-injection in addition to main injection, and sub-injection is performed according to the temperature of the NOx catalyst. There is something that changes the timing.
[0008]
However, none of these prior arts has an idea of refreshing the catalyst by using a delay period of a change in the intake charge amount with respect to a change in the throttle opening at the time of switching from the stratified combustion mode to the uniform combustion mode.
[0009]
In view of the above circumstances, the present invention effectively utilizes the delay period of the change in the intake charge amount when switching from the stratified combustion mode to the uniform combustion mode, while ensuring combustibility and preventing a sudden change in torque, It is an object of the present invention to provide a control device for a spark ignition direct injection engine that can enhance the effect of promoting the release of NOx from the NOx catalyst and the reduction of the released NOx.
[0010]
[Means for Solving the Problems]
  The present invention includes an NOx catalyst for storing NOx in an oxygen-excess atmosphere and releasing NOx as the oxygen concentration decreases in an exhaust passage of an engine, and an injector for directly injecting fuel into a combustion chamber. The stratified charge combustion mode in which fuel is injected in the compression stroke while making the air fuel ratio larger than the stoichiometric air fuel ratioRatio andIn addition, the combustion state can be changed to the uniform combustion mode in which fuel is injected in the intake stroke, and the intake air amount adjusting means is controlled so as to reduce the intake charge amount when switching from the stratified combustion mode to the uniform combustion mode. In the spark ignition direct injection engine in which the air-fuel ratio is adjusted by the above, when the switching from the stratified combustion mode to the uniform combustion mode, the intake air amount adjusting means is controlled in the direction of decreasing the intake air amount, and then the actual intake air charge amount The delay means for delaying the time to switch the fuel injection from the injector to the intake stroke injection by the time until the fuel pressure decreases to an appropriate value in the uniform combustion mode, and during the delay period by this delay means, In addition to fuel injection, fuel injection in the expansion stroke is performed, and the air-fuel ratio in the combustion chamber by the compression stroke injection is the stoichiometric air-fuel ratio. Even while increasing Ri, the air-fuel ratio of the exhaust gas by the compression stroke injection and an expansion stroke injection is the stoichiometric air-fuel ratioLess thanAnd a mode switching control means for controlling so as to become (Claim 1).
[0011]
  According to this device, when switching from the stratified combustion mode to the uniform combustion mode, the period when the actual intake charge amount is larger than the appropriate value in the uniform combustion mode due to the delay of the intake system with respect to the control of the intake air amount adjusting means In addition, the compression stroke injection and the expansion stroke injection are performed, and the air-fuel ratio in the combustion chamber by the compression stroke injection is made lean, so that combustibility by stratified combustion is ensured and a sudden increase in torque is prevented. Moreover, when the intake charge amount is increased due to the delay of the intake system when switching to the uniform combustion mode as described above, the air-fuel ratio of the exhaust is made rich in the compression stroke injection and the expansion stroke injection. A large amount of rich air-fuel ratio exhaust gas is supplied to the NOx catalyst, and release and reduction of NOx are promoted.
  Further, according to this apparatus, during the delay period, the CO and HC in the exhaust gas increase, and the release of NOx from the NOx catalyst and the reduction of the released NOx are promoted. Emission is suppressed.
[0014]
  In the present invention, the stratified combustion mode is executed in this region with the predetermined low load region as the stratified combustion region, and the uniform combustion mode is executed in this region with the operation region on the higher load side as the uniform combustion region. In this case, the delay by the delay means and the control by the mode switching time control means may be performed at the time of acceleration from the stratified combustion region to the uniform combustion region.2).
[0015]
In this way, when accelerating from the stratified combustion region, control is performed so that the intake charge gradually increases as the target load increases until the transition to the uniform combustion region. Even after the intake air amount adjusting means is controlled in the decreasing direction, the actual intake charge increase trend continues to some extent due to the delay of the intake system, and thus the above-mentioned mode switching control is performed during the period when the intake charge amount increases. By performing the compression stroke injection and the expansion stroke injection by the means, the air-fuel ratio of the exhaust sent to the NOx catalyst is made rich and the amount of the exhaust gas is sufficiently increased to promote the release and reduction of NOx. Enhanced.
[0016]
  Alternatively, when the NOx storage amount of the NOx catalyst increases to a predetermined value or more during operation in the stratified combustion mode, the mode is changed to the uniform combustion mode only for a predetermined time for catalyst refresh that releases NOx from the NOx catalyst. In addition, when the switching from the stratified combustion mode for the catalyst refresh to the uniform combustion mode is performed, the delay by the delay unit and the control by the mode switching time control unit may be performed.3).
[0017]
In this way, when changing to the uniform combustion mode for the catalyst refresh during operation in the stratified combustion mode, the intake air amount adjustment means is controlled in the direction of decreasing the intake air amount while the actual intake air amount is decreased. In the period when the delay occurs, the compression stroke injection and the expansion stroke injection are performed by the control means at the time of the mode switching, and the uniform combustion is performed by the intake stroke injection below the stoichiometric air-fuel ratio after the intake charge amount is reduced. This facilitates the release of NOx from the NOx catalyst and the reduction of the released NOx (hereinafter referred to as catalyst refresh including the reduction of NOx) while ensuring the combustibility and adjusting the torque satisfactorily.
[0018]
  Claims above2In the present invention, as the control by the mode switching time control means, for example, the compression stroke injection amount is gradually increased until the middle of the delay period by the delay means, and the compression stroke injection amount is gradually decreased from the middle of the delay period. (Claims)4).
[0019]
By doing so, the compression stroke injection amount gradually increases until the middle of the delay period, so that the torque is gradually increased to match the increase in the target load due to acceleration. From the middle of the delay period, the compression stroke injection amount is increased. By suppressing this increase, over-rich around the spark plug and increase in the amount of NOx generated can be avoided.
[0020]
  In addition, the above claims2Or3In the present invention, the control by the mode switching time control means includes reducing the compression stroke injection amount from a value corresponding to the required torque during the delay period by the delay means and requesting the compression stroke injection and the expansion stroke injection. The expansion stroke injection amount may be controlled so that torque is obtained.5).
[0021]
In other words, if the expansion stroke injection is performed at a time close to the compression top dead center, the expansion stroke injection also contributes to torque generation to some extent. Therefore, the compression stroke injection is expected in consideration of the torque generation contribution of the expansion stroke injection. If the expansion stroke injection amount is adjusted so that the torque corresponding to the target load (required torque) can be obtained by reducing the amount and compressing stroke injection and expansion stroke injection, the torque adjustment and catalyst refresh can be performed well. Is called.
[0022]
  The mode switching control means may retard the ignition timing in addition to the fuel injection control during the delay period of the delay means.6). Alternatively, the mode switching control unit controls the EGR device that recirculates a part of the exhaust gas to the intake system in a state of performing the recirculation of the exhaust gas in addition to the control of the fuel injection during the delay period by the delay unit. (You may be able to7). In this way, NOx in the exhaust gas is reduced by ignition timing retard or exhaust gas recirculation, and the ratio of the CO amount and HC amount to the NOx amount increases, which is advantageous for improving the catalyst refresh performance.
[0023]
  The configuration of the engine control system in which the apparatus of the present invention is incorporated sets a target load based on the accelerator opening, determines a target air-fuel ratio for intake air amount control based on the target load and the engine speed, A target air-fuel ratio for injection amount control is obtained based on the intake air amount control means for controlling the intake air amount adjusting means in accordance with the air-fuel ratio, the value obtained by smoothing the target load and the detected value of the charging efficiency, and this target Fuel injection amount control means for calculating the fuel injection amount from the injector based on the air-fuel ratio (claims)8) Is preferable.
[0024]
In this way, the timing of the control of the intake amount with a low response speed and the control of the fuel injection amount with a high response speed are effectively adjusted, and torque shock and emission deterioration are prevented. Based on such control, the mode switching time control means is performed during a period when a response delay of the change in the intake charge amount occurs when switching from the stratified combustion mode to the uniform combustion mode. Torque adjustment is performed properly and catalyst refresh is promoted.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the overall structure of an in-cylinder injection engine to which the present invention is applied. In this figure, the engine body 10 has a plurality of cylinders 12, and each cylinder 12 is formed with a combustion chamber 15 above a piston 14 inserted into the cylinder bore. And the exhaust ports open, and these ports are opened and closed by an intake valve 17 and an exhaust valve 18, respectively.
[0026]
A spark plug 20 is disposed at the center of the combustion chamber 15, and the tip of the plug faces the combustion chamber 15. In addition, the front end of the injector 22 faces the combustion chamber 15 from the side, and fuel is directly injected into the combustion chamber 15 from the injector 22. A fuel circuit having a high-pressure fuel pump, a pressure regulator, etc. (not shown) is connected to the injector 22 so that fuel is supplied to the injector 22 of each cylinder and the fuel pressure is higher than the in-cylinder pressure in the compression stroke. The fuel circuit is configured so that
[0027]
An intake passage 24 and an exhaust passage 31 are connected to the engine body 10. The intake passage 24 is provided with an air cleaner 25, an air flow sensor 26, a throttle valve 28 driven by a motor 27 and a surge tank 29 in that order from the upstream side. The throttle valve 28 and a motor 27 for driving the throttle valve 28 are provided. Thus, the intake air amount adjusting means is configured.
[0028]
The exhaust passage 31 is provided with a NOx catalyst 33 for exhaust gas purification. This NOx catalyst 33 has NOx purification performance even in a lean operation state in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, occludes NOx in the exhaust gas in an oxygen-excess atmosphere, and the air-fuel ratio changes to the rich side. When the oxygen concentration is reduced, the stored NOx is released, and NOx is reduced by a reducing material such as CO present in the atmosphere.
[0029]
More specifically, the NOx catalyst 33 is layered on a carrier made of a cordierite honeycomb structure or the like, with the NOx occlusion material layer and the catalyst material layer facing down (inside) and the latter facing up (outside). It is formed. The NOx occlusion material layer is composed mainly of an active alumina having a large specific surface area supporting a Pt component and a Ba component as a NOx occlusion material. Further, the catalyst material layer is composed mainly of a catalyst material obtained by supporting zeolite as a support base material and supporting a Pt component and an Rh component thereon. A ceria layer may be formed on the catalyst material layer.
[0030]
Further, an EGR device that recirculates part of the exhaust gas to the intake system is provided between the exhaust passage 31 and the intake passage 24, and this EGR device connects the exhaust passage 31 and the intake passage 24. And an EGR valve 36 interposed in the EGR passage 35. The EGR valve 36 is driven by an actuator to open and close.
[0031]
In addition to the airflow sensor 26, the engine includes a boost sensor 40 that detects intake negative pressure in the surge tank 29, a throttle opening sensor 41 that detects the throttle opening, a rotation speed sensor 42 that detects the engine speed, Accelerator opening sensor 43 for detecting accelerator opening (accelerator operation amount), intake air temperature sensor 44 for detecting intake air temperature, atmospheric pressure sensor 45 for detecting atmospheric pressure, water temperature sensor 46 for detecting engine cooling water temperature, in exhaust gas Sensors such as an O2 sensor 47 that detects the air-fuel ratio by detecting the oxygen concentration of the sensor are provided, and output signals (detection signals) of these sensors are input to an ECU (control unit) 50.
[0032]
The ECU 50 controls the fuel injection amount and the injection timing from the injector 22 and controls the throttle valve 28 by outputting a control signal to the motor 27 that drives the throttle valve 28, and also controls the ignition circuit 21. The ignition timing is controlled by outputting a signal, and the EGR valve 36 is also controlled.
[0033]
As basic control of the direct injection engine of this embodiment, a predetermined low load region is a stratified combustion region, and a region on the higher load side is a uniform combustion region. In the stratified combustion region, the fuel is injected from the injector 22 in the latter stage of the compression stroke, so that the stratified combustion mode is set such that combustion is performed in a stratified state where the air-fuel mixture is unevenly distributed in the vicinity of the spark plug 20, In this case, the air-fuel ratio of the entire combustion chamber becomes a lean state (for example, 30 or more) by increasing the opening of the throttle valve 28 and increasing the intake air amount. On the other hand, in the uniform combustion region, fuel injection is started from the injector 22 in the first half of the intake stroke while the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio (the excess air ratio λ is ≦ 1). In this state, the combustion is performed in a state where the air-fuel mixture is uniformly diffused.
[0034]
FIG. 2 shows a configuration of means functionally included in the ECU 50. The ECU 50 has an intake density state detection means 51 that detects an intake density state based on signals from the intake temperature sensor 44 and the atmospheric pressure sensor 45, and uses signals from the accelerator opening sensor 43 and the engine speed sensor 42. Based on the intake air density state, there is a target load setting means 52 for setting a value corresponding to the target load.
[0035]
When the target load setting means 52 assumes standard operating conditions for maintaining the air-fuel ratio at the theoretical air-fuel ratio from the virtual volume efficiency obtained from the map according to the accelerator opening degree accel and the engine speed ne and the intake density state. The charging efficiency corresponding to the required engine torque is calculated as the virtual charging efficiency, and the target indicated mean effective pressure, which is a value corresponding to the virtual charging efficiency, is determined as the target load.
[0036]
In this case, the first target indicated average effective pressure Piobj is obtained by a predetermined calculation, while the virtual filling efficiency is subjected to the annealing process, and the second target indicated average effective pressure Piobjd is calculated from the virtual filling efficiency after the annealing process. Is starting to ask.
[0037]
The ECU 50 further includes an operation mode setting means 53. The operation mode setting means 53 sets a basic operation mode mods according to the first target indicated mean effective pressure Piobj and the engine speed ne. That is, as shown in FIG. 3, in the region where the first target indicated mean effective pressure Piobj is lower than the set value and the engine speed ne is lower than the set speed (stratified combustion region), the stratified combustion mode is set. In a higher load side and higher rotation side region (uniform combustion region), a uniform combustion mode (stoichiometric mode) of λ = 1 is set. Note that, in the uniform combustion region, the air-fuel ratio may be set richer (λ <1) than the stoichiometric air-fuel ratio in the accelerator fully open region and in the high load region and high rotation region in the vicinity thereof.
[0038]
Further, the ECU 50 sets the values of various control parameters such as the intake air amount adjusted by the throttle valve 28, the fuel injection amount and fuel injection timing from the injector 22, the EGR amount adjusted by the EGR valve 36, and the ignition timing of the spark plug 20. It is determined according to the target load and the engine speed ne. In this case, in order to adjust the timing of the control of the control parameter having a low response speed such as the intake air amount (low speed response system) and the control of the control parameter having a high response speed such as the fuel injection amount (high speed response system), the control parameter Among them, the first target indicated mean effective pressure Piobj is used as the target load for determining the control value of the low-speed response system, and the second target as the target load for determining the control value of the high-speed response system. The indicated mean effective pressure Piobjd is used.
[0039]
That is, among the above control parameters, the intake air amount and the EGR amount are low-speed response systems that have relatively low responsiveness to the operation of the throttle valve 28 and the EGR valve, respectively, and these control amounts are the throttle opening tvoobj and EGR. The control amount of the valve 36 is determined according to the first target indicated mean effective pressure Piobj, the engine speed ne, and the like. On the other hand, the fuel injection amount, the fuel injection timing, and the ignition timing are fast response systems that quickly respond to the control signal, and these fuel injection amount, fuel injection timing, and ignition timing are the second target indicated mean effective pressure Piobjd and the engine. It is determined according to the rotational speed ne and the like.
[0040]
More specifically, as means for controlling the intake air amount, a target air-fuel ratio setting means 54 and a throttle opening degree calculation means 55 are provided. The target air-fuel ratio setting means 54 sets the target air-fuel ratio afwb for intake air amount control for each operation mode mods set by the operation mode setting means 53. In the stratified combustion mode, the first target indicated average In accordance with the effective pressure Piobj and the engine speed ne, the target air-fuel ratio afwb is obtained from a map created in advance, and in the stoichiometric mode, the target air-fuel ratio afwb is set as the stoichiometric air-fuel ratio.
[0041]
The throttle opening calculation means 55 obtains the target charging efficiency from the virtual charging efficiency corresponding to the target load (a value corresponding to the target load assuming a state where the engine is operated at the theoretical air-fuel ratio) and the target air-fuel ratio afwb, The target volume efficiency is calculated from the target charging efficiency in consideration of the intake density correction, and the throttle opening is determined according to the target volume efficiency and the engine speed ne.
[0042]
Means for controlling fuel injection from the injector 22 includes target air-fuel ratio creation means 56, injection amount calculation means 57, injection timing setting means 58, and injection control means 59.
[0043]
The target air-fuel ratio creating means 56 obtains a target air-fuel ratio for control of the fuel injection amount, etc., obtains a transient target air-fuel ratio afw0, a steady-state target air-fuel ratio afwbd, and these target air-fuel ratios. Either afw0 or afwbd is selected to determine the final target air-fuel ratio afw.
[0044]
The target air-fuel ratio afw0 at the time of transition is calculated using the second target indicated average effective pressure Piobjd or the corresponding virtual charging efficiency and actual charging efficiency ce so that a torque corresponding to the target load can be obtained under the actual charging efficiency. Based on the fuel efficiency improvement effect. On the other hand, the target air-fuel ratio afwbd at the steady state is obtained from a map prepared in advance according to the second target indicated mean effective pressure Piobjd and the engine speed ne in the stratified combustion mode, and in the stoichiometric mode, the stoichiometric air-fuel ratio (Λ = 1). When the deviation dafwb between the target air-fuel ratio afwb for intake air amount control and the target air-fuel ratio afw0 becomes large, the target air-fuel ratio afw0 is made the final target air-fuel ratio afw, and when the deviation dafwb is small, the deviation dafwb The target air-fuel ratio afwbd is set as the final target air-fuel ratio afw.
[0045]
The injection amount calculating means 57 calculates a basic injection amount from the actual charging efficiency ce obtained from the output of the air flow sensor 26 and the target air-fuel ratio afw obtained by the target air-fuel ratio creating means 56, and further various correction values. In consideration of this, the final injection amount is calculated, and an injection pulse width Ti proportional to the final injection amount is obtained.
[0046]
The injection timing setting means 58 sets the fuel injection timing thtinj for each operation mode. In the stratified combustion mode, the injection timing setting means 58 is based on a map created in advance according to the second target indicated mean effective pressure Piobjd and the engine speed ne. The injection timing for compression stroke injection is obtained, and in the stoichiometric mode, the injection timing for intake stroke injection is obtained from a table prepared in advance according to the engine speed ne.
[0047]
The injection control means 59 applies the injection pulse so as to operate the injector 22 for the time corresponding to the injection pulse width Ti calculated by the injection amount calculation means at the injection timing set by the injection timing setting means 58. Output.
[0048]
Reference numeral 60 denotes ignition timing control means. In the stratified combustion mode, the basic ignition timing is obtained from the map according to the second target indicated mean effective pressure Piobjd and the engine speed ne, and in the stoichiometric mode, the actual charge amount and The basic ignition timing is obtained from the map according to ce and the engine speed ne, and the ignition timing is obtained from the basic ignition timing and various correction values according to the water temperature and the like. Reference numeral 61 denotes EGR control means. In the stratified combustion mode, the basic EGR valve control amount is obtained from the map according to the first target indicated mean effective pressure Piobj and the engine speed ne, and in the stoichiometric mode, the actual charging amount and ce are obtained. The basic EGR valve control amount is obtained from the map in accordance with the engine speed ne, the EGR valve control amount is calculated by adding various correction values to the basic EGR valve control amount, and the control signal corresponding thereto is calculated as EGR. It outputs to the valve 36.
[0049]
Further, in addition to the above means, the ECU 50 is provided with a delay means 63 and a mode change time control means 65 in order to promote the refresh of the catalyst when the stratification mode is switched to the uniform mode.
[0050]
When the operation mode set by the operation mode setting unit 53 is switched from the stratified combustion mode to the uniform combustion mode, the delay unit 63 starts control for reducing the throttle opening and reducing the intake charge amount. The time for switching the fuel injection from the injector 22 to the intake stroke injection is delayed by the time until the actual intake charge amount decreases to an appropriate value in the uniform combustion mode.
[0051]
Further, the mode switching time control means 65 changes the control by the injection control means 59 during the delay period by the delay means 63, and performs fuel injection from the injector 22 in the expansion stroke in addition to the fuel injection in the compression stroke. Make it. That is, as shown in FIG. 4, the fuel injection from the injector 22 is controlled by compression stroke injection in the stratified combustion mode and intake stroke injection in the uniform combustion mode, but when switching from the stratified combustion mode to the uniform combustion mode. During the delay period, the expansion stroke injection is performed in addition to the compression stroke injection. The expansion stroke injection timing may be set, for example, as the first half of the expansion stroke close to the compression top dead center.
[0052]
When the compression stroke injection and the expansion stroke injection are performed during the delay period, the air-fuel ratio in the combustion chamber by the compression stroke injection is larger than the theoretical air-fuel ratio, and the exhaust gas by the compression stroke injection and the expansion stroke injection is increased. The respective injection amounts are controlled so that the air-fuel ratio becomes equal to or lower than the stoichiometric air-fuel ratio.
[0053]
The mode switching control means 65 changes the ignition timing control by the ignition timing control means 60 in addition to the fuel injection control as described above during the delay period by the delay means 63 to retard the ignition timing. Alternatively, the EGR valve 36 may be controlled via the EGR valve control means 61 so as to increase the EGR amount as compared with when in the uniform combustion mode.
[0054]
FIG. 5 is a flowchart mainly showing processing that performs the functions of the delay means 63 and the mode switching control means 65.
[0055]
When the processing of this flowchart is started, first, various signals such as engine speed, accelerator opening, air flow sensor output, water temperature, etc. are input in step S1, and then in step S2, operation is performed based on the target load and engine speed. The operation mode mods set by the mode setting means 53 is checked to determine whether or not it is the stratified combustion mode. If it is determined that the stratified charge combustion mode is selected, the compression stroke injection is performed in step S3.
[0056]
If it is determined in step S2 that the mode is not the stratified combustion mode (that is, the uniform combustion mode), it is determined in step S4 whether or not the previous time was the uniform combustion mode.
[0057]
When the determination in step S4 is NO, that is, when the stratified combustion mode is switched to the uniform combustion mode, the timer is set in step S5, and the compression stroke injection and the expansion stroke injection are performed in step S6. The time set by the timer is set to an extent corresponding to the time required for the intake charge amount to decrease to an appropriate value in the uniform combustion mode from the time when the operation mode is set by the operation mode setting means. The time required for the intake charge amount to decrease to an appropriate value in the uniform combustion mode from the time when this operation mode is changed varies depending on the engine speed. In step S5, it is desirable that the time corresponding to the engine speed at that time is obtained from the table and set in the timer.
[0058]
If the determination in step S4 is YES, it is determined in step S7 whether or not the timer is 0, so that the elapsed time from the time of switching to the uniform combustion mode is within the set time by the timer. It is investigated whether or not. And if the elapsed time from the said switching time is less than setting time, it will move to step S6 and the state in which compression stroke injection and expansion stroke injection are performed will be maintained.
[0059]
When the determination in step S7 is NO, that is, when the elapsed time from the switching time exceeds the set time, intake stroke injection is performed as normal control in the uniform combustion mode in step S8.
[0060]
The effect | action by the apparatus of this embodiment is demonstrated more concretely, referring the time chart of FIG.
[0061]
In the stratified combustion region on the low load side where the accelerator opening is small and the charging efficiency is low, the air-fuel ratio (A / F) is made lean, and the fuel is injected from the injector 22 in the compression stroke. The stratified combustion state is advantageous for improvement. During the lean operation by stratified combustion, NOx in the exhaust gas is occluded in the NOx catalyst 33.
[0062]
When an acceleration operation is performed by depressing the accelerator pedal from this state, as shown in FIG. 6, while in the stratified combustion region, the throttle opening is increased corresponding to the increase in the accelerator opening from the acceleration operation start time t0. The filling efficiency gradually increases as it gradually increases. When the target load (first target indicated mean effective pressure Piobj) that increases in accordance with the accelerator opening becomes equal to or greater than a predetermined value and shifts to the uniform combustion region, the throttle is opened to enrich the air-fuel ratio at that time t1. However, due to a temporary delay in the intake system, the charging efficiency ce gradually increases after it has increased to some extent even after the throttle opening becomes small, and the charging efficiency ce reaches the steady state value in the uniform combustion mode. There is a considerable delay time to get close enough.
[0063]
Therefore, the time T from the time t1 when the throttle opening is reduced to the time t2 when the charging efficiency decreases within the appropriate range in the uniform combustion mode (from the steady state value in the uniform combustion mode to the predetermined range) (FIG. 5). The switching to the intake stroke injection for achieving a uniform combustion state is delayed by the time set in the step S5 in the middle).
[0064]
During this delay period T, the fuel injection from the injector 22 is controlled so that the compression stroke injection and the expansion stroke injection are performed. In this case, the air-fuel ratio in the combustion chamber by the compression stroke injection is made leaner than the theoretical air-fuel ratio (A / F = 14.7) as shown by a broken line a in FIG. As shown by the solid line b, the air-fuel ratio of the exhaust gas due to both the expansion stroke injection is made rich below the stoichiometric air-fuel ratio, so that combustibility is ensured and sudden torque change is prevented. The catalyst refreshing effect of releasing and reducing the catalyst is enhanced.
[0065]
In other words, in order to enhance the catalyst refresh effect, it is effective to enrich the air-fuel ratio of the exhaust to increase CO and HC as reducing materials in the exhaust. However, if the air-fuel ratio by compression stroke injection is enriched, the ignition Around the plug becomes overrich, and the flammability deteriorates. Also, if the air-fuel ratio is enriched by switching to the uniform combustion state by the intake stroke injection, combustibility is secured, but the intake charge amount is excessive compared to the appropriate value in the uniform combustion mode due to the primary delay of the intake system In order to enrich the air-fuel ratio during the delay period T in this way, it is necessary to increase the fuel injection amount, resulting in a rapid increase in torque.
[0066]
On the other hand, in the apparatus of the present invention, stratified combustion is performed at the lean air-fuel ratio by the compression stroke injection during the delay period T, so that combustibility is ensured even in an excessive intake state and a sudden increase in torque is avoided. In addition, the expansion stroke injection is performed in addition to the compression stroke injection, so that the air-fuel ratio of the exhaust is made rich and the refreshing of the NOx catalyst is promoted. In particular, since the air-fuel ratio of the exhaust gas is made rich during the delay period in which the charging efficiency is high due to the primary delay of the intake system, the uniform combustion mode after the charging efficiency is lowered (after the delay period T has elapsed) Compared with the case where the air-fuel ratio is enriched, the amount of exhaust gas at the rich air-fuel ratio increases, so the amount of CO and HC supplied to the NOx catalyst 33 increases, and the NOx release and reduction action is enhanced. Become.
[0067]
Further, in the apparatus of the present embodiment, the throttle opening according to the target air-fuel ratio afwb for intake air amount control set based on the first target indicated mean effective pressure Piobj corresponding to the target load and the engine speed ne On the other hand, the control of the fuel injection amount at the time of transition is performed for the injection amount control transient obtained based on the second target indicated mean effective pressure Piobjd (the smoothed target load) and the charging efficiency ce. Since the process is performed in accordance with the target air-fuel ratio afw0 at the time, the air-fuel ratio and the torque are appropriately adjusted even during a transient, and torque shock and emission deterioration are prevented. Based on such control, it is also possible to appropriately control the fuel injection amount during the delay period when switching from the stratified combustion mode to the uniform combustion mode.
[0068]
For example, the injection amount calculated in accordance with the target air-fuel ratio afw0 at the time of transient for the above-described injection amount control is set as the compression stroke injection amount, and the injection amount and the compression required to obtain a predetermined rich air-fuel ratio equal to or lower than the target air-fuel ratio. An amount corresponding to the difference from the stroke injection amount may be the expansion stroke injection amount.
[0069]
In other words, the transient target air-fuel ratio afw0 obtained by the target air-fuel ratio creating means 56 is obtained so that torque corresponding to the target load can be obtained under the actual charging efficiency. The target air-fuel ratio afw0 is made lean so that the torque corresponding to the target load can be obtained under the situation where the charging efficiency is higher than that of. Since the compression stroke injection mainly contributes to the compression stroke injection among the compression stroke injection and the expansion stroke injection, the injection amount is set according to the target air-fuel ratio afw0, and the compression stroke injection is thus performed. If the expansion stroke injection amount is set so that the air-fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air-fuel ratio while setting the amount, torque adjustment and catalyst refresh can be performed satisfactorily.
[0070]
In the control during the delay period, until the middle of the delay period, the compression stroke injection amount may be gradually increased to increase the torque according to the increase in the target load due to the acceleration operation. Therefore, in order to avoid over-rich around the spark plug and increase in the amount of NOx generated, it is preferable to control so as to suppress the increase in the compression stroke injection amount.
[0071]
Further, by performing the expansion stroke injection at a time close to the compression top dead center, the expansion stroke injection can also contribute to torque generation to some extent. In this case, in consideration of the torque generation contribution of the expansion stroke injection, the compression stroke injection amount is a value corresponding to the target air-fuel ratio afw0 (a value for obtaining a torque corresponding to the target load under the actual charging efficiency). ), And the expansion stroke injection amount may be adjusted so that a torque (required torque) corresponding to the target load is obtained by the compression stroke injection and the expansion stroke injection.
[0072]
Further, if the ignition timing is retarded in addition to the fuel injection control as described above during the delay period, the amount of NOx discharged from the combustion chamber decreases, so the ratio of the CO amount and the HC amount to the NOx amount ( (CO / NOx, HC / NOx) becomes larger, thereby further enhancing the effect of promoting the release and reduction of NOx from the NOx catalyst 33. Even if EGR is performed instead of or in addition to the ignition timing retard, CO / NOx and HC / NOx increase due to the reduction of NOx in the exhaust gas, and the catalyst refresh effect is enhanced.
[0073]
In the above embodiment, the NOx catalyst 33 is refreshed at the time of acceleration from the stratified combustion region to the uniform combustion region. However, the NOx occlusion amount of the NOx catalyst exceeds a predetermined value during the lean operation in the stratified combustion mode. When the state increases, the NOx catalyst is refreshed by changing to the uniform combustion mode in which the intake stroke injection is performed at the stoichiometric air-fuel ratio or less for a predetermined time, and the stratified combustion mode in this case is made uniform. At the time of switching to the combustion mode, the delay by the delay means and the control by the mode change time control means may be performed.
[0074]
That is, when the operation in the stratified combustion region is continued and the mode is switched to the uniform combustion mode for refreshing the NOx catalyst, the intake air charging is performed in contrast to the control in which the throttle opening is reduced to enrich the air-fuel ratio. Although there is a delay in the decrease in the amount, the compression stroke injection and the expansion stroke injection are performed during the delay period, so that the combustibility is ensured and the torque fluctuation is suppressed, and the catalyst refresh effect is achieved. Will be enhanced.
[0075]
【The invention's effect】
As described above, according to the present invention, in the direct injection engine equipped with the NOx catalyst, the intake charge amount decreases after the intake amount adjustment means is controlled in the intake charge amount decrease direction when switching from the stratified combustion mode to the uniform combustion mode. In the delay period until the compression stroke injection, the expansion stroke injection is performed in addition to the compression stroke injection, and the air-fuel ratio in the combustion chamber by the compression stroke injection is larger than the theoretical air-fuel ratio, and the exhaust by the compression stroke injection and the expansion stroke injection is performed. Since the air-fuel ratio of the engine is less than the stoichiometric air-fuel ratio, while taking advantage of the fact that the intake charge amount increases during the delay period while ensuring the combustibility and performing the torque adjustment at the time of mode switching, It is possible to supply a large amount of rich air-fuel ratio exhaust gas to the NOx catalyst, thereby promoting the release and reduction of NOx and enhancing the catalyst refresh effect.
[0076]
In particular, if the control by the delay means and the control means at the time of mode switching is performed during acceleration when shifting from the stratified combustion region on the low load side to the uniform combustion region on the high load side, the transition to the uniform combustion region is achieved by acceleration. This increases the amount of exhaust gas with a rich air-fuel ratio supplied to the NOx catalyst and greatly enhances the catalyst refresh effect. it can.
[Brief description of the drawings]
FIG. 1 is an overall schematic view showing an embodiment of an apparatus of the present invention.
FIG. 2 is a block diagram showing a functional configuration of an ECU.
FIG. 3 is an explanatory diagram showing region setting for an operation mode.
FIG. 4 is an explanatory diagram showing the timing of fuel injection.
FIG. 5 is a flowchart showing a specific example of control.
FIG. 6 is a time chart showing changes in various control parameters and the like when switching from a stratified combustion mode to a uniform combustion mode by an acceleration operation;
[Explanation of symbols]
10 Engine body
15 Combustion chamber
20 Spark plug
22 Injector
24 Intake passage
31 Exhaust passage
33 NOx catalyst
36 EGR valve
50 ECU
63 Delay means
65 Control means at mode switching

Claims (8)

The exhaust passage of the engine is provided with a NOx catalyst that stores NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases, and an injector that directly injects fuel into the combustion chamber. with a changeable combustion state to the homogeneous combustion mode for injecting fuel in a more greatly while the intake stroke while the stratified combustion mode and the air-fuel ratio for injecting fuel to the theoretical air-fuel ratio in the compression stroke, the stratified charge combustion mode In a spark ignition direct injection engine in which the air-fuel ratio is adjusted by controlling the intake air amount adjusting means so as to reduce the intake charge amount when switching to the uniform combustion mode, the stratified combustion mode is changed to the uniform combustion mode. At the time of switching, the actual intake charge amount is reduced to an appropriate value in the uniform combustion mode after the intake amount adjustment means is controlled in the direction of decreasing the intake charge amount. The delay means for delaying the time to switch the fuel injection from the injector to the intake stroke injection for the time until the fuel injection, and the fuel in the expansion stroke in addition to the fuel injection from the injector in the compression stroke during the delay period by this delay means The air-fuel ratio in the combustion chamber by the compression stroke injection is made larger than the stoichiometric air-fuel ratio, and the exhaust air-fuel ratio by the compression stroke injection and the expansion stroke injection is smaller than the stoichiometric air-fuel ratio. A control device for a spark ignition type direct injection engine, comprising: a mode switching control means for controlling the engine. The stratified combustion mode is executed in this region with the predetermined low load region as the stratified combustion region, while the homogeneous combustion mode is executed in this region with the operation region on the higher load side as the uniform combustion region. 2. The control device for a spark ignition type direct injection engine according to claim 1, wherein the control by the delay means and the mode change time control means is performed at the time of acceleration from the region to the uniform combustion region. When the NOx storage amount of the NOx catalyst increases to a predetermined value or more during operation in the stratified combustion mode, control is performed to change to the uniform combustion mode for a predetermined time for catalyst refresh that releases NOx from the NOx catalyst. 2. The spark ignition method according to claim 1, wherein when the switching is performed from the stratified combustion mode for the catalyst refresh to the uniform combustion mode, the delay by the delay means and the control by the mode switching time control means are performed. Control device for direct injection engine. The mode switching time control means controls to gradually increase the compression stroke injection amount until the middle of the delay period by the delay means and gradually decrease the compression stroke injection amount from the middle of the delay period. Item 3. A spark ignition direct injection engine control device according to Item 2. The mode switching control means reduces the compression stroke injection amount from a value corresponding to the required torque during the delay period of the delay means, and expands so that the required torque can be obtained by the compression stroke injection and the expansion stroke injection. 4. The control device for a spark ignition direct injection engine according to claim 2, wherein the stroke injection amount is controlled. 6. The spark ignition type direct injection according to claim 1, wherein the mode switching time control means retards the ignition timing in addition to the fuel injection control during the delay period of the delay means. Engine control device. The mode switching control means controls the EGR device that recirculates a part of the exhaust gas to the intake system in a state in which the exhaust gas recirculates in addition to the control of fuel injection during the delay period by the delay means. The control device for a spark ignition direct injection engine according to any one of claims 1 to 6. A target load is set based on the accelerator opening, a target air-fuel ratio for intake air amount control is obtained based on the target load and the engine speed, and an intake air amount for controlling the intake air amount adjusting means in accordance with the target air-fuel ratio A target air-fuel ratio for injection amount control is obtained based on the control means, the value obtained by smoothing the target load and the detected value of the charging efficiency, and the fuel injection amount from the injector is calculated based on the target air-fuel ratio. The control device for a spark ignition type direct injection engine according to any one of claims 1 to 7, further comprising fuel injection amount control means.

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